This invention relates to a method for manufacturing electrically insulating composite materials with a high specific modulus of elasticity and high dielectric strength, consisting of a cross-linked epoxy resin or epoxy resin mixture and a fiber reinforcement based on synthetic polymers.
In electrotechnology, insulating parts of high mechanical strength and low density in the form of composite materials are frequently required, e.g. laminates of a resin matrix and reinforcement fibers. This applies, for instance, to hollow-cylindered tie rods or plungers which are used in high-voltage circuit breakers, especially if switching gaps at high-voltage potential are to be switched by a drive at ground potential.
With switching gap distances of up to several meters, insulating tube materials with a small ratio of wall thickness to diameter are required in order to obtain advantageous physical dimensions while maintaining as low a weight as possible. Composite materials or laminates containing glass fibers and unsaturated polyester resins or glass fibers and epoxy polyaddition resins have an average density of 1.8 g cm.sup.-3. By using synthetic polymer fiber materials, the laminate density can be reduced, on average, to 1.3 g cm.sup.-3. Unfortunately, the advantages of such fibers, namely, low density and high tensile strength can not be utilized due to the lack of suitable impregnating resin systems.
Insulating tube materials and rods for high-voltage circuit breakers are known, for instance, from German Pat. No. 22 64 341 (see col. 1, lines 4 to 10) and DE-AS 24 29 475 (see col. 1, lines 3 to 21). In the manufacture of these tubes or rods a casting resin which is hardenable by polyaddition, usually an epoxy resin, is used. An insulating woven fabric material is embedded in the resin. These fabrics are sometimes made of plastic or glass fibers. The resulting compositions suffer from inadequate bonding between the resin and fiber components.